In Scientific Controversies, hosted by our own Janna Levin, we tackle complex, conceptual, occasionally amorphous topics like dark energy and string theory. These rich, hour-long conversations take place in person at Pioneer Works, and feature big thinkers exchanging on big questions. To watch is a feast. “5 Takeaways” is a snack, an amuse-bouche for the mind. Because comprehension sometimes demands—or, at the very least, appreciates—distillation, and the internet loves a listicle. Below, for the benefit of lay science enthusiasts, contributor Anil Ananthaswamy serves up key takeaways from a conversation between Janna and neuroscientists Anil Seth and Joseph LeDoux on the body, brain, and consciousness.

What is consciousness?

Well, that’s a tough question. There are probably as many answers as there are philosophers and neuroscientists theorizing about consciousness. To help keep our feet planted on scientific ground, let’s talk about consciousness as the brain-generated subjective experience of something, anything: the smell of a flower, the color of the sky, even the feeling of being someone with a body and a story. You could imagine building a robot with today’s technology that has the sensors to sense the electromagnetic spectrum of the sky. Does it have an internal experience of the sky being blue on a clear winter’s day? Very likely not. But we do. Let’s call that a conscious experience. It doesn’t matter what one is conscious of; the contents of one’s consciousness aren’t important. The subjective feeling, the experience of that content, can be attributed to consciousness.

Why is it subjective?

Because each one of us is a distinct individual with a distinct body and brain. The brain has no direct access to the world outside or even to the rest of the body, except via the information carried by nerves from within the body and without. The brain has to infer what’s out there based solely on such incoming information. Computational neuroscientists think that the most efficient way for the brain to make such inferences is by predicting the external causes of incoming information, using internal models it builds of the body and of the environment. These predictions are what we perceive, consciously or otherwise. Let’s say you and I are looking at a rose. Firstly, each of our brain’s predictions of the rose’s redness may not tally with objective reality. Also, because our brains are different, in their wiring and biochemical makeup, their predictions will likely differ ever-so-slightly. We just agree to call the rose ‘red’; we have no idea if we are talking of the same kind of redness. Also, the experience is being had by an experiencing self. So, in all these ways, it’s subjective.

What is the Self?

The self is another thorny word, with myriad meanings. We can start by distinguishing the self from self-consciousness, which is the awareness of being a self. Let’s worry about the former; the latter can be understood as some higher order outcome of the former. The basic self is best thought of as the entity that experiences. Again, the exact experience is not important: it could be a color, a sound, or pain in one’s left foot. But in all cases, there seems to be an entity experiencing it. So, the self, in its stripped-down form can be thought of as the subject of an experience. Of course, then the question arises: is such an experiencing entity itself a construction or prediction? Some neuroscientists think so. It might be that it’s the outcome of an internal model or self-schema built by the brain.

Do animals have selves and are they conscious?

Opinions vary. Before talking of animals, consider the Roomba scuttling about in your living room. It certainly has a self-model, meaning a model of its shape, size, speed, etc. situated within an internal model of the room. Almost no neuroscientist or philosopher in their right mind would say that the Roomba is conscious or has self-consciousness. But such statements become blurrier when talking about apes, dogs, cats or more primitive animals. Given that animals navigate physical spaces and survive, they most certainly possess a self-model. They are also most likely conscious, but the contents of their consciousness—meaning what it feels like to be a cat or a dog or a bonobo having some experience—will be different from ours and indeed from each other’s. Self-consciousness, however, is harder to pin down; the great apes are almost certainly self-aware. Opinions begin differing when considering other animals. And then there are octopuses, with a highly distributed nervous system; their behaviors have all the hallmarks of highly intelligent, conscious beings. No one disputes their intelligence, but are they conscious? The honest answer: we don’t know.

How can we tell if an animal is conscious, or has a self?

It’s well-nigh impossible to tell if an animal is conscious. For that matter, we cannot be sure of each other’s consciousness. Maybe one day there will be an objective measure of consciousness, based on brain activity. For now, we can agree that humans are conscious beings, because we can say so to each other. Interrogating the presence of a self is somewhat easier, but only just about. There’s the mirror self-recognition (MSR) test: while an animal is under anesthesia, an experimenter puts a colored dot on the animal’s forehead. When the animal comes to, it’s shown a mirror. If it recognizes in the mirror a reflection of itself, the animal will touch its forehead and the dot, maybe even remove the dot. If it does so, it clearly has a form of self-awareness. A handful of species pass the test, including the great apes, dolphins and a species of magpie. Most fail the test. But the MSR test is controversial. For starters, a mark on the forehead may not elicit the desired response simply because the mark isn’t threatening. So, failing the test doesn’t imply lack of self-awareness; it just means that the animal couldn’t be bothered. Also, MSR only tests for whether or not animals have visual self-awareness. Maybe most don’t. Maybe they use other sensory information, such as smells or sounds, to construct self-models and distinguish themselves from others. Simply put, consciousness and the self remain enigmatic. ♦